1. Field of the Invention
The present invention relates to a projector and, particularly, to a projector having a focus ring.
2. Description of the Background Art
There has been a projector as one of devices for projecting a picture on a screen. A lens main body for projecting a picture is attached to the projector. As shown in FIG. 10, a focus ring 102 is generally attached to a lens main body 105. Lens main body 105 with focus ring 102 has a diameter larger than that of lens main body 105 without focus ring 102, thereby easily achieving focusing.
In lens main body 105, a lens itself is attached to a projection ring 103. Projection ring 103 is provided with a protrusion 103a protruded outwardly.
On the other hand, focus ring 102 is provided with a slit 104 for receiving protrusion 103a. Slit 104 includes: an opening 102a for receiving protrusion 103a; and a passage 102b which is narrower than opening 102a. Focus ring 102 is generally made of resin.
Next, description will be given of a procedure of attaching focus ling 102. First, an entering portion of passage 102b of focus ring 102 is brought into contact with protrusion 103a from a direction shown by an arrow mark, and focus ring is pushed in the same direction. At this time, passage 102b is widened, so that protrusion 103a passes through passage 102b and is received by opening 102a. 
With this structure, focus ring 102 is attached and fixed to projection ring 103. In this state, focus ring is turned in a circumferential direction, so that lens main body is also turned. As a result, focusing can be achieved in the projector.
However, the conventional projector has the following problems. As shown in FIG. 10, when focus lens 102 is attached to lens main body 105, focus lens 102 has to be positioned in the circumferential direction such that the position of slit 104 coincides with that of protrusion 103a. 
Therefore, in the case where it is difficult to observe the position of protrusion 103 from the outside of the projector, it takes a long time to attach focus lens 102 to lens main body 105 in some cases.
In addition, as shown in FIG. 11, in the case where focus ring is molded with resin, a die 114 is used for particularly molding opening 102a. As shown in FIG. 12, since three slits 104 are provided on focus ring 102 in the circumferential direction, die 114 has to be detached in three directions as shown by arrow marks 111, 112, 113, respectively. Therefore, a problem has arisen in that the structure of the die is complicated.